The trouble is that sex can become boring time and time again with same partner.... you kind of know what to expect and there aren't any big surprises. There is nothing new brought into the relationship.... thus it becomes repetitious and boring. Fooling around with multiple partners is just not a good idea today...it's too risky. You got too much to lose.
I'm going to say that great sex begins with a little variety....something a little different each time. This requires work from both partners.
The next thing I will say is that great foreplay is where it is at. Foreplay can feel better and be almost even more rewarding than the actual cllmax. Women need up to twenty minutes of foreplay to become fully aroused. Men can be manually brought up several times before actually having intercourse and ejaculating. "Bottom" line.... if you are having sex in 10 minutes or less, you need to make it last much longer!